The invention relates to a system for adjusting the tension of the belt of a continuously variable transmission.
Such a system is described in FIG. 1 and is known, for example, from EP-A-0 451 887. This publication too relates to the adjustment of the tension of a belt means 1, usually a belt, in a continuous belt transmission 2 comprising belt means 1, a drive pulley 3 and an output pulley 4 which is driven by an engine 11.
To adjust the transmission ratio of a continuously variable belt transmission and the tension of the belt means 1, the drive pulley 3 comprises an axially stationary conical pulley half 7 and an axially movable conical pulley half 9 and the output pulley 4 comprises an axially stationary conical pulley half 8 and an axially movable conical pulley half 10. The drive pulley 3 is also known as the primary pulley and the output pulley 4 is also known as the secondary pulley. Pressing of the axially movable conical pulley halves 9 and 10 against the belt means 1 takes place in response to the build-up of a hydraulic pressure in the respective oil chambers 5 and 6. The desired transmission ratio of the continuously variable belt transmission and the required tension of the belt means 1 can be adjusted by a suitable selection of the applied pressures Pprim and Psec in the oil chambers 5 and 6. For the force transmission from the engine 11 to the drive pulley 3, for example, a torque converter 12 and a planetary assembly 13 can be provided with clutches for forward and rearward travel. The engine 11 can also drive the pump 14 of the continuously variable belt transmission. A transmission control 18 comprises the electrical and hydraulic components for driving the continuously variable belt transmission. The transmission control 18 includes means for adjusting the pressure in the oil chamber 6 or in the oil chambers 5 and 6.
The tension of the belt means 1 is adjusted in one embodiment of the transmission control 18 utilizing the pressure Psec in the output end oil chamber 6.
The tension of the transmission means 1 is to be so adjusted that the efficiency of the continuously variable belt transmission is a maximum. On the one hand, it is to be prevented that the belt means 1 slips because of too low a tension and, on the other hand, the tension of the belt means 1 should not be too high in order to avoid high losses in the continuously variable belt transmission. To reconcile the two requirements, the torque transmitted from the drive pulley 3 to the output pulley 4 must be known as precisely as possible. The torque to be transmitted on the drive pulley 3 is determined primarily by the torque of the engine 11 and the torque amplification factor of the torque converter 12.
In U.S. Pat. No. 5,337,628 a method for adjusting the pressure Psec in the output end oil chamber 6 is described. In this method, the rotational angle xcex1Dk of the throttle flap 15 of the engine 11 is detected by a sensor 16. Furthermore, the rpm Nmot of the engine 11, the rpm Nprim of the primary pulley 3 and the rpm Nsec of the secondary pulley 4 are measured with rpm sensors 19, 20 and 21 and conducted as corresponding signals to the transmission control 18. The angle position xcex1Dk of the throttle flap is measured by the sensor 16. The angle position xcex1Dk, the engine rpm Nmot, the primary rpm Nprim, and the secondary rpm Nsec are utilized in the transmission control 18 to adjust the tension of the belt means 1 by adjusting the pressure in the oil chamber 6.
To adjust the tension of the belt means 1, the engine torque to be expected is estimated with a characteristic field of the throttle flap angle and the engine rpm. The engine torque to be expected is converted into an expected primary torque in a characteristic field with the formed quotient of the primary rpm and the engine rpm. Thereafter, the computation of the required pressure Psec takes place in the output end oil chamber to adjust the tension of the belt element 1.
The use of the throttle flap angle xcex1Dk to estimate the torque has the disadvantage that the calibration of the throttle flap potentiometer must take place very precisely. Even a small deviation of the measured throttle flap angle from the actual throttle flap angle can, in the above method, lead to a considerable deviation between the expected engine torque and the actual engine torque. It is difficult to guarantee that the throttle flap angle will always be measured correctly. For this reason, the belt tension must be held above the required level with a higher safety reserve in that a pressure higher about the reserve pressure is adjusted in the output end oil chamber. This leads to higher losses in the transmission and in the pump. Furthermore, problems can occur for the estimate of the engine torque during dynamic driving conditions with greater time-dependent changes of the engine rpm.
U.S. Pat. No. 6,050,913 improves the above-mentioned adjustment of the belt tension in that, for example, a torque value, which is computed in the engine control apparatus, is applied to adjust the belt tension. Embodiments for determining the safety reserve are not be found.
In modern-day engine control systems, a detection of combustion misfires of one or several cylinders of the vehicle is mostly in use which computes an engine rough running value from fluctuations of the engine rpm. This value is compared to the applied threshold values. A combustion misfire is detected when the engine rough running exceeds the threshold value. For this purpose, reference is made to German patent publication 4,138,765. Problems can be caused in this context by various disturbance quantities on the engine rpm signal. Such disturbance quantities are, for example, mechanical defects of the transducer wheel in detecting engine rpm, charge differences of the individual cylinders (differences because of the combustion process) and torsion vibrations. These disturbance influences are adapted in normal operation for precise misfire detection which is described in German patent publication 196 22 448 and in European patent publication 0,733,890. This means that, after a completed adaptation, corrective values are available which are considered for a precise detection of the engine rpm.
Furthermore, distance control systems are known from the state of the art, for example, from the publication mot, no. 15, Jun. 11, 1998. These distance control systems detect the distance of a vehicle to a vehicle traveling ahead. In general, this takes place via a radar sensor. If the distance becomes too little, then these systems provide for brake interventions independent of the driver.
The task of the present invention comprises optimizing the belt tension and especially determining the safety reserve.
As already mentioned, the invention proceeds from a system for adjusting the tension of the belt part (for example, the band) of a belt transmission mounted downstream of the vehicle engine and preferably a belt transmission which is continuously adjustable in its transmission ratio. First means for controlling (open loop and/or closed loop) the vehicle engine and second means for controlling (open loop and/or closed loop) of the continuously variable transmission are provided. With the first means, a first signal is determined which represents the engine torque of the vehicle engine and is supplied by the first means to the second means. With the second means, the tension is then adjusted in dependence upon the first signal and a safety reserve.
The essence of the invention comprises that this safety reserve is not fixedly pregiven; instead, this safety reserve is determined in dependence upon various conditions. For this reason, one reaches a reduction of the lump-sum reserve pressure of the belt tension control and thereby an improved transmission efficiency and thereby a reduced consumption of fuel.
In a first embodiment of the invention, it is provided that, via the first means, a second signal is determined which represents the quality of the first signal. This second signal is then supplied from the first means to the second means whereupon the safety reserve is determined in dependence upon the second signal. The belt part, that is, the band, is thereby protected from excessive wear in situations wherein the engine torque is uncertain.
In a second embodiment of the invention, means are provided with which a deterioration value is determined which represents the wear and/or the deterioration of the belt part. The safety reserve is then determined in dependence upon the deterioration value. This embodiment considers that the contact pressure, which is necessary to avoid slip, is greatly dependent upon the deterioration or the wear of the belt part. This means that a new belt requires less contact pressure for the transmission of the same engine torque than an already deteriorated/worn belt. With the invention, one arrives at an optimized adaptation of the belt tension to the state of the belt.
In a third embodiment of the invention, three means are provided via which a third signal is determined. This third signal represents the brake action, which is to be adjusted at the vehicle wheels, and/or the yaw movement and/or the transverse movement of the vehicle. The third signal is then supplied by the third means to the second means and the safety reserve is determined in dependence upon the third signal. The advantage of this configuration comprises that abrupt torque changes which operate at the transmission output end are detected. In this way, provision can be made in time for increasing the belt tension.
A fourth embodiment of the invention provides that the second means is supplied with a fourth signal representing the rotational speed or the change of the rotational speed of at least one vehicle wheel. The safety reserve is then determined in dependence upon the fourth signal. In a similar manner as for the third embodiment, the background of this embodiment is that a conclusion can be drawn from the dynamic of the vehicle wheels as to abrupt torque changes which act at the output end of the transmission. If the wheel dynamic indicates such torque changes, then an increase of the belt tension can be advantageously and timely provided.
In a fifth embodiment of the invention, it is provided that fourth means are provided for the distance control mentioned initially which determines an intervention signal in dependence upon the detected distance to a vehicle traveling ahead. With this intervention signal, an intervention into the brake system of the vehicle is triggered or prepared. According to the invention, the safety reserve is determined in dependence upon the intervention signal. Abrupt torque changes, which act at the output end of the transmission, or torque in-couplings at the transmission can be caused also by brake interventions for the distance control. For this reason, it is advantageous to consider these torque changes in the determination of the belt tension.
In a sixth embodiment of the invention, it is provided that fifth means are provided which determine a roadway value at least by means of a sensor and this roadway value represents the unevenness of the roadway to be traveled by the vehicle. In this connection, a radar sensor can be considered having output signals which are applied also the initially-mentioned distance control. The safety reserve is determined in dependence upon the roadway value. This configuration is based on the consideration that abrupt torque changes at the transmission output and therefore at the belt can also occur because of an uneven roadway. In this case, the belt tension has to be correspondingly increased in order to prevent damage of the belt.
For the first embodiment, it can be provided that the second signal represents a quality of at least possible fluctuations of the first signal, that is, of the engine torque.
Here it is advantageously considered that the second signal (that is, the quality of the engine torque) is determined in dependence upon the tolerances of at least one sensor whose output signal is evaluated for controlling (open loop and/or closed loop) the vehicle engine. In this connection, it can be especially provided that:
the first sensor functions for the direct or indirect detection of the air mass supplied to the engine;
the sensor serves for detecting a temperature, which is evaluated for controlling (open loop and/or closed loop) the vehicle engine; and/or,
the sensor serves to detect characteristics of the exhaust gas of the vehicle engine whose output signals are applied especially for detecting the air/fuel mixture supplied to the vehicle engine.
The sensor for direct or indirect detection of the air mass, which is supplied to the vehicle engine, can, for example, be configured as a hot-film air-mass sensor, an intake manifold pressure sensor or as a throttle flap potentiometer for measuring the angular position of the throttle flap.
In a further advantageous variation of the first embodiment, the second signal is determined in dependence upon a detected fault function in the operation of the vehicle engine. Here, it is especially provided that a fault function is then detected when:
combustion misfires are detected in one or several of the cylinders of the vehicle engine, especially by evaluating the detected engine rpm; and/or,
a fault function of a sensor is detected whose output signal is evaluated for controlling (open loop and/or closed loop) the vehicle engine; and/or,
an emergency operation of the first means is present and especially an electrical emergency; and/or,
the fuel supply to individual cylinders of the vehicle engine is interrupted in reaction to a detected fault.
In another advantageous variation of the first embodiment, the second signal is determined in dependence upon the detected rough running of the vehicle engine. Here, it is especially provided that the detection of the rough running is dependent upon whether:
mechanical vibrations, especially torsion vibrations, are present in the drive train of the vehicle; and/or,
the fuel supply to the individual cylinders of the engine is interrupted; and/or,
the first means controls (open loop and/or closed loop) the engine in such a manner that vibrations in the drive train are countered (anti-jolt function, load-impact damping); and/or,
a switchover between various modes of operation of the engine of the vehicle takes place; and/or,
a detection is made that a pregivable quality of the roadway is present (detection of a poor roadway); and/or,
the fuel tank is almost empty.
A switchover between various modes of operation of the vehicle engine can, for example, be a switchover between a homogeneous operation and a stratified operation of the engine in engines having direct gasoline injection.
Here, it can be provided that the second signal is determined in dependence upon stored adaptation values which represent the rough running of the vehicle engine wherein the adaptation values can be stored in dependence upon load and/or rpm.
In a last advantageous variation of the first embodiment, the second signal is determined in dependence upon inaccuracies which occur in the determination of the first signal. In this connection, the following can be provided:
that the second signal is determined in dependence upon the rpm of the vehicle engine; and/or,
that, via the first means, an adaptation of the friction torque (that is, lost torques), especially at idle of the vehicle engine, is performed and the second signal is determined in dependence upon whether the adaptation is completed or not.
For the second embodiment, it can be provided that the deterioration value is determined in dependence upon the service life of the belt part. Here, it is especially provided that the deterioration value is further determined in dependence upon the operating conditions which are present during the duration of operation with these operating conditions including the driving performance of the driver, operating temperature and/or slippage of the belt part.
Here, it can be further provided that the deterioration value is determined in the second means and is there non-volatilely stored.
As a fourth embodiment, it can be provided that the fourth signal is supplied to the second means by the third means and the third means is configured as an anti blocking control system and/or a drive slip control system and/or a driving stability control system with which a brake torque, which operates on the vehicle wheels, can be adjusted for increasing driving stability.
For the sixth embodiment, it can be provided that at least one clutch is provided in the drive train of the vehicle and that the clutch is opened in dependence upon the roadway value and on detected fault cases, especially combustion misfires. Here, especially a converter bridging clutch can be considered via which a torque converter, which is provided in the drive train, can be bridged. Such an opening of the converter clutch can also be advantageous in the detection of combustion misfires described in the first embodiment.
Advantageously, and according to the invention, the safety reserve is determined as follows:
in the first embodiment, the tension of the belt part is increased when a lower quality of the first signal is present compared to the adjustment of the tension for the presence of a higher quality of the first signal;
in the second embodiment, the tension of the belt part is increased when a higher wear is present and/or a deterioration to a greater extent compared to the adjustment of the tension for the presence of a lower wear and/or a deterioration of a lesser extent;
in the third embodiment, the tension of the belt part is increased when a brake action or a yaw movement and/or a transverse movement of greater extent is present compared to the adjustment of the tension for the presence of a braking action and/or a yaw movement and/or a transverse movement of a lesser extent;
in the fourth embodiment, the tension of the belt part is increased for the presence of a higher rpm or the greater change of the rpm of at least of one of the wheels of the vehicle compared to the adjustment of the tension for the presence of a lower rpm or the smaller change of the rpm;
for the fifth embodiment, the tension of the belt part is increased for the presence of a braking intervention triggered by the fourth means (102); and,
in the sixth embodiment, the tension of the belt part is increased for the presence of an unevenness of the roadway of greater extent compared to the adjustment of the tension for the presence of an unevenness of lesser extent.
It is especially advantageous that first a voltage value is determined which is dependent upon the first signal, that is, on the engine torque. This base value is then modified or increased in dependence upon the safety reserve. Here, it is especially provided that the adjustment of the tension takes place hydraulically and the tension is adjusted by the input of at least one pressure value. Depending on the first signal, a pressure value (base value) is determined which is modified or increased in dependence upon the safety reserve.